This disclosure relates to a medical device and more particularly to an implantable therapeutic substance delivery device with a piston-operated pump.
The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions such as pacemakers, defribulators, neurostimulators, and therapeutic substance delivery pumps. Medical devices can be configured to be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with therapeutic substance therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Implantable drug delivery pumps can be used to treat conditions such as pain, spasticity, cancer, and a wide variety of other medical conditions.
An implantable drug delivery pump is implanted by a clinician into a patient at a location appropriate for the therapy that interferes as little as practicable with patient activity such as subcutaneous in the lower abdomen. Typically, a drug delivery catheter is connected to the drug pump outlet and implanted to infuse the drug, infusate or other therapeutic substance at a programmed infusion rate and predetermined location to treat the medical condition. Reliable and accurate operation of the drug pump is important because both inadequate and unintended therapeutic substance delivery can create patient complications. Many drug pumps are configured, so the pump can be replenished with drug through a refill port or septum while the pump is implanted, so the period the pump can be implanted may not be limited by drug capacity. In electrically powered implantable drug pumps, the period the pump can be implanted is often limited by factors such as battery consumption, corrosive damage, and mechanical wear. The relative large size of some implantable drug pumps can limit locations where the device can be implanted in a patient. An example of an implantable drug pump is shown in Medtronic, Inc. “SynchroMed® Infusion System” Product Brochure (1995). Implantable drug pumps can use a variety of pumping mechanism such as a piston pump, rotary vane pump, osmotic pump, Micro Electro Mechanical Systems (MEMS) pump, diaphragm pump, peristaltic pump, and solenoid piston pump to infuse a drug into a patient.
Piston pumps such as variable reluctance piston pumps and piston pumps operate by applying an electromagnetic force to a pump piston. The electromagnetic force imparts movement to the pump piston to pump fluid from a pumping chamber into an outlet. Although the fluid flowing into a pumping chamber is controlled with a flow restrictor or an inlet valve, the fluid flowing into an inlet chamber is not typically controlled. Without a control such as valve on fluid flowing into the inlet chamber, fluid in the inlet chamber can backflow when the inlet chamber fluid is compressed to fill the pumping chamber. Backflow of fluid from the inlet chamber can cause low pumping chamber pressures that when the pumping chamber is being filled with fluid that in turn can cause gasses to come out of solution in the fluid. Additionally backflow of fluid out of the inlet chamber causes pump operation to be less efficient because fluid is being moved in and out of the inlet chamber for no operating purpose. An example of a previous piston pump with an inlet flow restrictor is shown in U.S. Pat. No. 4,883,467 “Reciprocating Pump For An Implantable Medication Dosing Device” by Franetzki et al. (Nov. 28, 1989), and an example of a previous piston pump inlet valve is shown in U.S. Pat. No. 4,636,150 “Low Power Electromagnetic Pump” by Falk et al. (Jan. 13, 1987).
For the foregoing reasons, there is a need for an anti-cavitation valve for a piston pump therapeutic substance delivery device that reduces gas formation, increases accuracy, improves efficiency and has many other improvements.